不用max函数返回表中最大值或者最小值
返回Test表中字段num的最大值或者最小值（不用Max函数）, 为了好玩。：)
- 返回最大值
select distinct num from Test where num not in ( select lesser.num from Test as greater,Test as lesser where lesser.num<greater.num)
- 返回最小值
select distinct num from Test where num not in ( select greater.num from Test as greater,Test as lesser where lesser.num<greater.num)
原因是以下SQL返回的结果集中，lesser.num中包括所有num除了最大值，greater.num中包括所有num除了最小值：
select lesser.num,greater.num from Test as lesser, Test as greater where lesser.num < greater.num;